I am trying to develop a publish/subscribe system.
To this end, I have read some papers and articles regarding it.
And they all talk about Messaging service as an integral part of publish/subscribe system.
My question is, can I develop a publish subscribe system without using MOM like JMS? Or am I missing or oversimplifying things?
I do not think you are oversimplifying things. There are stand-alone products available that provide advanced functionality based on publish/subscribe, without being part of a larger MOM system.
One of them is a group of products implementing the Data Distribution Service (DDS) specification, as standardized by the Object Management Group (OMG). Check out this Wikipedia entry for a very brief introduction and list of references.
DDS supports many advanced data management features like a strong-typed and content aware databus, distributed state management and historical data access. Its rich set of Quality of Service settings allows to off-load a lot of the complexity from your applications to the middleware. This is all based on the publish/subscribe paradigm.
If you would tell more about your application, then I might be able to point you to similar use cases using this technology -- if you are interested.